Eccentric oscillation type speed reducer

ABSTRACT

An eccentric oscillation type speed reducer includes: an internal gear; an external gear which meshes with the internal gear; an eccentric body shaft which oscillates the external gear; and a carrier disposed at a side portion of the external gear in an axial direction, in which the carrier includes a first carrier which is disposed on one side in the axial direction of the external gear, and a second carrier which is disposed on the other side in the axial direction of the external gear, a driven member is connected to the first carrier, the first carrier is made of metal, and the second carrier is made of resin.

RELATED APPLICATIONS

Priority is claimed to Japanese Patent Application No. 2018-034330,filed Feb. 28, 2018, the entire content of which is incorporated hereinby reference.

BACKGROUND Technical Field

Certain embodiments of the present invention relate to an eccentricoscillation type speed reducer.

Description of Related Art

In the related art, the applicant of this application disclosed aplanetary speed reducing mechanism provided with an external gear whichis oscillated by an eccentric body, and an internal gear with which theexternal gear internally meshes.

SUMMARY

According to an embodiment of the present invention, there is providedan eccentric oscillation type speed reducer including: an internal gear;an external gear which meshes with the internal gear; an eccentric bodyshaft which oscillates the external gear; and a carrier disposed at aside portion of the external gear in an axial direction, in which thecarrier includes a first carrier which is disposed on one side in theaxial direction of the external gear, and a second carrier which isdisposed on the other side in the axial direction of the external gear,a driven member is connected to the first carrier, the first carrier ismade of metal, and the second carrier is made of resin.

According to another embodiment of the present invention, there isprovided an eccentric oscillation type speed reducer including: aninternal gear provided in a casing; an external gear which meshes withthe internal gear; an eccentric body shaft which oscillates the externalgear; and a carrier disposed at a side portion of the external gear inan axial direction, in which the casing and the external gear are madeof resin, and the carrier is made of metal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side sectional view showing an eccentric oscillation typespeed reducer according to one embodiment.

FIG. 2 is a sectional view taken along line A-A of the eccentricoscillation type speed reducer of FIG. 1.

FIG. 3 is a side sectional view showing an eccentric oscillation typespeed reducer according to another embodiment.

DETAILED DESCRIPTION

The planetary speed reducing mechanism of the related art is providedwith two flanges, casings, or the like, as main constituent elements, inaddition to the external gear and the internal gear. In the speedreducing mechanism of the related art, since these main constituentelements are made of a steel material, the weight of the speed reducingmechanism tends to increase. Regarding such a speed reducing mechanism,it is required to reduce weight in order to expand the use.

It is desirable to provide an eccentric oscillation type speed reducerwhich can be reduced in weight, which has been made in view of suchproblems.

According to an embodiment, since the first carrier to which the drivenmember is connected is made of metal, it is possible to obtain requiredstrength or rigidity, and since the second carrier is made of resin, areduction in weight can be made.

Any combination of the above constituent elements or mutual substitutionof constituent elements or expressions of the present invention betweenmethods, systems, or the like is also effective as an aspect of thepresent invention.

Hereinafter, the present invention will be described with reference tothe respective drawings, based on preferred embodiments. In anembodiment, a comparative example, and a modification example, identicalor corresponding constituent elements and members are denoted by thesame reference numerals, and overlapping description is appropriatelyomitted. Further, the dimensions of members in each drawing are shown inan appropriately enlarged or reduced manner for easy understanding.Further, in each drawing, some of members which are not important fordescribing an embodiment are omitted in illustration.

Further, terms including ordinal numbers such as first, second, or thelike are used to describe various constituent elements. However, theseterms are used only for the purpose of distinguishing one constituentelement from the other constituent element, and the constituent elementsare not limited by these terms.

One Embodiment

Hereinafter, the configuration of an eccentric oscillation type speedreducer 10 according to one embodiment will be described with referenceto FIGS. 1 and 2. FIG. 1 is a side sectional view showing the eccentricoscillation type speed reducer 10 of one embodiment. FIG. 2 is asectional view of the eccentric oscillation type speed reducer 10 takenalong line A-A of FIG. 1. In these drawings, for easy understanding, oneof two external gears 14 is shown and the other is not shown. The otherexternal gear 14 is different from one external gear 14 in that it has aphase difference of 180 degrees, and the other configurations are thesame. The eccentric oscillation type speed reducer 10 of this embodimentis an eccentric oscillation type speed reducer which oscillates anexternal gear which meshes with an internal gear, thereby causing one ofthe external gear and the internal gear to rotate, and outputs thegenerated motion component from an output member to a driven device.

The eccentric oscillation type speed reducer 10 mainly includes an inputshaft 12, the external gear 14, an internal gear 18, carriers 18 and 20,a casing 22, main bearings 24 and 25, an inner pin 40, and a carrier pin38. Hereinafter, a direction along a central axis La of the internalgear 16 is referred to as an “axial direction”, and a circumferentialdirection and a radial direction of a circle centered on the centralaxis La are respectively referred to as a “circumferential direction”and a “radial direction”. Further, in the following, for convenience,one side in the axial direction (the right side in the drawing) isreferred to as an input side and the other side (the left side in thedrawing) is referred to as an anti-input side.

Input Shaft

The input shaft 12 is rotated around a rotation center line by therotational power which is input from a driving device (not shown). Theeccentric oscillation type speed reducer 10 of this embodiment is acenter crank type in which the rotation center line of the input shaft12 is provided on the same axis as the central axis La of the internalgear 16. The driving device is, for example, a motor, a gear motor, anengine, or the like.

The input shaft 12 in this embodiment is an eccentric body shaft havinga plurality of eccentric portions 12 a for oscillating the external gear14. There is a case where the input shaft 12 having such a configurationis referred to as a crankshaft. The axis of the eccentric portion 12 ais eccentric with respect to the rotation center line of the input shaft12. In this embodiment, two eccentric portions 12 a are provided, andthe eccentric phases of the eccentric portions 12 a adjacent to eachother are shifted by 180°.

The input side of the input shaft 12 is supported on a second cover 23through an input shaft bearing 34, and the anti-input side thereof issupported on the first carrier 18 through the input shaft bearing 34.That is, the input shaft 12 is supported so as to be rotatable withrespect to the first carrier 18 and the second cover 23. Theconfiguration of the input shaft bearing 34 is not particular limited.However, in this example, the input shaft bearing 34 is a ball bearinghaving a spherical rolling element. Pressurization may be applied to theinput shaft bearing 34. However, in this example, pressurization is notapplied thereto.

External Gear

The external gear 14 is individually provided corresponding to each ofthe plurality of eccentric portions 12 a. The external gear 14 isrotatably supported on the corresponding eccentric portion 12 a throughthe eccentric bearing 30. As shown in FIG. 2, twelve through-holes areformed at equal intervals in the external gear 14 at positions offsetfrom the axis of the external gear 14. The carrier pins 38 are insertedinto three holes disposed at equal intervals of 120 degrees, among thethrough-holes, and the inner pins 40 are inserted into the remainingnine holes. For this reason, the former is referred to as a carrier pinhole 39 and the latter is referred to as an inner pin hole 41. Theseholes may have the same diameter. However, in this example, the diameterof the carrier pin hole 39 is larger than the diameter of the inner pinhole 41.

The carrier pin hole 39 and the inner pin hole 41 are circular holesprovided at the same radial position. Wavy teeth are formed on the outerperiphery of the external gear 14, and this tooth moves while cominginto contact with an internal tooth 16 a of the internal gear 16, sothat the external gear 14 can oscillate in a plane with a center axis asa normal line. The inner pin hole 41 through which the inner pin 40passes is formed in the external gear 14. A clearance which serves as aplay for absorbing an oscillation component of the external gear 14 isprovided between the inner pin 40 and the inner pin hole 41. The innerpin 40 and the inner wall surface of the inner pin hole 41 partiallycome into contact with each other.

Internal Gear

The internal gear 16 meshes with the external gear 14. The internal gear16 in this embodiment has the internal teeth 16 a formed integrally withthe inner peripheral portion of the casing 22. That is, in this example,the internal teeth 16 a are portions seamlessly provided with respect tothe casing 22. In this embodiment, the number of internal teeth 16 a ofthe internal gear 16 is one more than the number of external teeth ofthe external gear 14.

Carrier

The carriers 18 and 20 are disposed at side portions of the externalgear 14 in the axial direction. The carriers 18 and 20 include a firstcarrier 18 which is disposed at the side portion on the anti-input sideof the external gear 14, and a second carrier 20 which is disposed atthe side portion on the input side of the external gear 14. The firstcarrier 18 and the second carrier 20 are rotatably supported on thecasing 22 through the first main bearing 24 and the second main bearing26. Each of carriers 18 and 20 has a disk shape as a whole. The firstcarrier 18 rotatably supports the input shaft 12 through the input shaftbearing 34. The second carrier 20 may be configured to support the inputshaft through the input shaft bearing. However, in this example, thesecond carrier 20 does not support the input shaft bearing 34 and theinput shaft 12.

The first carrier 18 and the second carrier 20 are connected to eachother through the carrier pin 38 and the inner pin 40. The carrier pin38 and the inner pin 40 axially penetrate the plurality of externalgears 14 at positions offset in the radial direction from the axis ofthe external gear 14. In this example, the carrier pin 38 and the innerpin 40 are provided separately from the carriers 18 and 20. However,some of these pins may be integrally formed as part of the carriers 18and 20. The carrier pin 38 and the inner pin 40 will be described later.

One of the first carrier 18 and the casing 22 functions as an outputmember which outputs rotational power to the driven device, and theother functions as a fixed member which is fixed to an external memberfor supporting the eccentric oscillation type speed reducer 10. Theoutput member is rotatably supported on the fixed member through themain bearings 24 and 26. In this embodiment, the output member is thefirst carrier 18 and the fixed member is the casing 22. A driven member50 which is rotationally driven by the eccentric oscillation type speedreducer 10 is connected to the end face on the anti-input side of thefirst carrier 18 by bolts 50 b.

Casing

The casing 22 has a hollow tubular shape as a whole, and the internalgear 16 is provided at the inner peripheral portion thereof. A flange orthe like may be provided at the outer peripheral portion of the casing22. However, in this example, the flange is not provided. The casing 22is provided with a first cover 21 which covers the anti-input side ofthe casing 22, and the second cover 23 which covers the input side ofthe casing 22. The first cover 21 and the second cover 23 are fixed tothe casing 22 by a plurality of bolts arranged in the circumferentialdirection.

The casing 22 is provided with a recessed portion which accommodates theinput side of an outer ring of the first main bearing 24. The firstcover 21 is provided with a recessed portion which accommodate a part onthe anti-input side of the outer ring of the first main bearing 24. Theouter ring of the first main bearing 24 is axially sandwiched andsupported between the casing 22 and the first cover 21. The casing 22 isprovided with a recessed portion which accommodates the input side of anouter ring of the second main bearing 26. The second cover 23 isprovided with a recessed portion which accommodate a part on theanti-input side of the outer ring of the second main bearing 26. Theouter ring of the second main bearing 26 is axially sandwiched andsupported between the casing 22 and the second cover 23. The secondcover 23 is provided with a recessed portion which accommodates an outerring of the input shaft bearing 34 on the input side. That is, thesecond cover 23 rotatably supports the input side of the input shaft 12through the input shaft bearing 34.

Main Bearing

The main bearings 24 and 26 include the first main bearing 24 which isdisposed between the first carrier 18 and the casing 22, and the secondmain bearing 26 which is disposed between the second carrier 20 and thecasings 22. Each of the main bearings 24 and 26 in this embodiment isprovided with a plurality of rolling elements 42 and a retainer (notshown). The plurality of rolling elements 42 are provided at intervalsin the circumferential direction. The rolling element 42 in thisembodiment is a spherical body. The retainer holds the relativepositions of the plurality of rolling elements 42 and rotatably supportsthe plurality of rolling elements 42.

Each of the main bearings 24 and 26 in this embodiment is provided withan outer ring 48 and an inner ring 49 having rolling surfaces for therolling element 42. The inner ring rolling surface may be provided onthe outer peripheral surface of each of the carriers 18 and 20, insteadof the inner ring. The outer ring 48 is fixed to the casing 22 byfitting such as a clearance fit, an interference fit, or a transitionfit. The fitting gap may be set corresponding to the difference inthermal expansion coefficient. Precompression may be applied to the mainbearings 24 and 26. However, in this example, precompression is notapplied thereto.

Inner Pin

As shown in FIG. 1, the inner pin 40 is inserted into the inner pin hole41 penetrated and formed in the external gear 14 with a gaptherebetween. One end of the inner pin 40 is fitted into a recessedportion 18 b of the first carrier 18, and the other end is fitted into arecessed portion 20 b of the second carrier 20. The inner pin 40 ispress-fitted into the recessed portions 18 b and 20 b and is not fixedby bolts or the like. The inner pin 40 is in contact with a part of theinner pin hole 41 formed in the external gear 14 and restrains therotation of the external gear 14 to allow only the oscillation thereof.The inner pin 40 functions as a connecting member which contributes totransmission of power between the first carrier 18 and the secondcarrier 20, and the external gear 14.

Carrier Pin

The carrier pin 38 is inserted into the carrier pin hole 39 penetratedand formed in the external gear 14 with a gap therebetween. One end ofthe carrier pin 38 is fitted into a recessed portion 18 c of the firstcarrier 18, and the other end is fitted into a recessed portion 20 c ofthe second carrier 20. The carrier pin 38 is press-fitted to therecessed portions 18 c and 20 c and is not fixed by bolts or the like.The carrier pin 38 is surrounded by a tubular spacer 37. One end of thespacer 37 is in contact with the first carrier 18 and the other end isin contact with the second carrier 20. The spacer 37 functions as aspacer for maintaining the axial distance between the first carrier 18and the second carrier 20 at an appropriate distance. The carrier pin 38and the spacer 37 are not in contact with the carrier pin hole 39 of theexternal gear 14 and do not contribute to restraining the rotation ofthe external gear 14. The carrier pin 38 functions as a connectingmember which contributes only to the connection between the firstcarrier 18 and the second carrier 20.

Next, a material configuring each constituent member of this embodimentwill be described. In recent years, the use of speed reducers hasexpanded to collaborative robots or the like, which operate near aperson. In order to expand the use, a reduction in the weight and areduction in noise of the speed reducer are desired. Speed reducers ofthe related art are configured with constituent members made ofiron-based metal, and thus, for a reduction in weight, it is conceivableto form the constituent members from materials with low specificgravity. As such a material, resin or the like is suitable. On the otherhand, if the constituent members are made of resin, it is conceivablethat a temperature rises due to a decrease in heat dissipation property,so that a lifetime is shortened. For this reason, it is conceivable tosuppress a rotational speed and an output torque to a low level inconsideration of the temperature rise.

Further, when the speed reducer is used for a robot, there is a casewhere it is easy to use carrier output due to the configuration thereof.In a case where a carrier on the load side is made of resin, in order tosecure the strength of a tap for mounting a driven member, it isconceivable to embed a female screw made of iron by insert molding. Inthis case, weight increases due to the female screw made of iron, andthe number of manufacturing processes increases due to the insertmolding.

From these viewpoints, the first carrier 18 in this embodiment is madeof metal, and the second carrier 20 is made of resin. In this case,since the first carrier 18 to which the driven member 50 is connected ismade of metal, it is possible to secure the strength of the tap formounting. Further, since the second carrier 20 is made of resin, theweight of the second carrier 20 can be reduced.

Various resins can be used for the second carrier 20. However, in thisexample, the second carrier 20 is made of polyacetal (POM). POM issometimes referred to as PO. From the viewpoint of alleviating theinfluence of a temperature rise, the second carrier 20 in thisembodiment is not in direct contact with the input shaft bearing 34 andis provided in a non-contact manner.

The resin which is used for each constituent member of this embodimentmay be resin containing reinforcing fibers such as glass fibers orcarbon fibers, may be resin which does not contain reinforcing fibers,and may be a material obtained by impregnating a base material such aspaper or cloth with resin and laminating it.

High-speed rotation before speed reduction is input to the input shaft12 and the input shaft bearing 34 which is disposed between the firstcarrier 18 and the input shaft 12. For this reason, a temperature riseof these elements is relatively large, and if heat resistance of theseelements is low, an allowable input rotational speed becomes low. Forthis reason, the input shaft bearing 34 and the input shaft 12 may bemade of metal. In this case, it is possible to suppress a decrease inthe allowable input rotational speed. Since a large torsional stress isapplied to the input shaft 12, it is preferable that the input shaft 12is made of a material having higher rigidity than the first carrier 18.Therefore, in this embodiment, the first carrier 18 is made of aluminum(including an aluminum alloy, hereinafter, the same) having high heatdissipation property, and the input shaft 12 is made of iron-based metalhaving higher torsional strength than aluminum.

As the iron-based metal which is used for each constituent member ofthis embodiment, carbon steel, bearing steel, stainless steel, or thelike can be used according to desired characteristics.

Since the external gear 14 is disposed in the vicinity of the inputshaft 12 with a large temperature rise, it is desirable that the heatresistance temperature of the external gear 14 is high. From thisviewpoint, the external gear 14 may be made of resin having a higherheat resistance temperature than the second carrier 20. In this example,the external gear 14 is made of polyetheretherketone (PEEK).

In order to secure the connection strength between the first carrier 18and the second carrier 20, it is desirable that the carrier pin 38 hashigh rigidity. From this viewpoint, the carrier pin 38 is made of metal,and the spacer 37 may be made of resin for a reduction in weight. Inthis example, the carrier pin 38 is made of iron-based metal and thespacer 37 is made of POM.

Since the input shaft 12 is subjected to a large torsional stress as theeccentric body shaft, it is desirable that the input shaft 12 is made ofa material having higher rigidity than the first carrier 18. It isdesirable that the first carrier 18 is made of a material having asmaller specific gravity than the input shaft 12 for a reduction inweight. From this viewpoint, the first carrier may be made of metalhaving a specific gravity of 5 or less, and the input shaft 12 may bemade of iron-based metal. The first carrier 18 may be made of lightmetal (metal having a specific gravity of 4 to 5 or less) such asaluminum, magnesium, beryllium, or titanium, or a composite materialthereof. In this example, the first carrier 18 is made of aluminum.

From the viewpoint of a reduction in weight, the casing 22, the firstcover 21, and the second cover 23 may be made of resin. These may bemade of the same resin or may be made of different resins. In thisexample, the casing 22 is made of PEEK, and the first cover 21 and thesecond cover 23 are made of POM.

As described above, in this embodiment, the external gear 14, the secondcarrier 20, the casing 22, the first cover 21, the second cover 23, andthe spacer 37 are made of resin. Further, the main bearings 24 and 26,the eccentric bearing 30, the input shaft bearing 34, the carrier pin38, the inner pin 40, the input shaft 12, and the bolt 50 b are made ofiron-based metal. Further, the first carrier 18 is made of light metalsuch as aluminum. Some or all of these constituent members of thisembodiment may be made of other materials.

The operation of the eccentric oscillation type speed reducer 10configured as described above will be described. If the rotational poweris transmitted from the driving device to the input shaft 12, theeccentric portion 12 a of the input shaft 12 rotates around the rotationcenter line passing through the input shaft 12, and the external gear 14oscillates due to the eccentric portion 12 a. At this time, the externalgear 14 oscillates such that its own axis rotates around the rotationcenter line of the input shaft 12. If the external gear 14 oscillates,the meshing position between the external gear 14 and the internal gear16 is sequentially shifted. As a result, each time the input shaft 12rotates once, one of the external gear 14 and the internal gear 16rotates by an amount corresponding to the difference in the number ofteeth between the external gear 14 and the internal gear 16. In thisembodiment, the external gear 14 rotates on its own axis, and adecelerated rotation is output from the first carrier 18.

Another Embodiment

Next, the configuration of an eccentric oscillation type speed reducer10 according to another embodiment will be described. In the drawing anddescription of another embodiment, constituent elements and membersidentical or corresponding to those in one embodiment are denoted by thesame reference numerals. Description overlapping that of one embodimentwill be appropriately omitted and the configurations different fromthose in one embodiment will be mainly described. FIG. 3 is a sidesectional view showing the eccentric oscillation type speed reducer 10of another embodiment and corresponds to FIG. 1.

In the description of one embodiment, the center crank type eccentricoscillation type gear device has been shown as an example. However theeccentric oscillation type speed reducer of this embodiment is aso-called distribution type eccentric oscillation type gear device. Theeccentric oscillation type speed reducer 10 of this embodiment is mainlydifferent from that of one embodiment in that the eccentric oscillationtype speed reducer 10 of this embodiment includes a plurality of inputgears 70 and the configuration of the input shaft 12 in this embodimentis different from that in one embodiment.

The plurality of input gears 70 are disposed around the central axis Laof the internal gear 16. In this drawing, only one input gear 70 isshown. The input gear 70 is supported by the input shaft 12 which isinserted into a central portion of the input gear 70, and is provided soas to be rotatable integrally with the input shaft 12. The input gear 70meshes with an external teeth portion of a rotary shaft (not shown)which is provided on the central axis La of the internal gear 16. Therotational power is transmitted from a driving device (not shown) to therotary shaft, and the input gear 70 rotates integrally with the inputshaft 12 due to the rotation of the rotary shaft.

In this embodiment, a plurality of (for example, three) input shafts 12are disposed at intervals in the circumferential direction at positionsoffset from the central axis La of the internal gear 16. In thisdrawing, only one input shaft 12 is shown.

The operation of the eccentric oscillation type speed reducer 10 of thisembodiment described above will be described. If the rotational power istransmitted from the driving device to the rotary shaft, the rotationalpower is distributed from the rotary shaft to the plurality of inputgears 70, and the respective input gears 70 rotate in the same phase. Ifeach input gear 70 rotates, the eccentric portion 12 a of the inputshaft 12 rotates around the rotation center line passing through theinput shaft 12, and the external gear 14 oscillates due to the eccentricportion 12 a. If the external gear 14 oscillates, similar to oneembodiment, the meshing position between the external gear 14 and theinternal gear 16 is sequentially shifted, and one of the external gear14 and the internal gear 16 rotates. The rotation of the input shaft 12is decelerated at a reduction ratio corresponding to the difference inthe number of teeth between the external gear 14 and the internal gear16 and is output from the output member to the driven device. The outputmember in this embodiment is also the first carrier 18.

In this embodiment, the external gear 14, the second carrier 20, thecasing 22, the first cover 21, the second cover 23, and the spacer 37are made of resin. Further, the main bearings 24 and 26, the eccentricbearing 30, the input shaft bearing 34, the carrier pin 38, the inputshaft 12, and the bolt 50 b are made of iron-based metal. Further, thefirst carrier 18 is made of light metal such as aluminum. Some or all ofthese constituent members of this embodiment may be made of othermaterials. In particular, the second carrier 20 may be made of resinhaving high heat resistance, such as PEEK.

The examples of embodiments of the present invention have been describedin detail above. All of the embodiments described above merely showspecific examples for implementing the present invention. The contentsof embodiments do not limit the technical scope of the presentinvention, and many design changes such as changes, additions, ordeletions of constituent elements can be made within a scope which doesnot depart from the idea of the invention defined in the claims. In theembodiment described above, the contents in which such a design changecan be made are described with the notation such as “of an embodiment”,or “in an embodiment”. However, it does not mean that a design change isnot permitted for contents without such notation. Further, the hatchingapplied to the cross-section of the drawing does not limit the materialof the hatched object.

Hereinafter, a modification example will be described. In the drawingand description of the modification example, constituent elements andmembers identical or corresponding to those in the embodiments aredenoted by the same reference numerals, and description overlappingthose of the embodiments will be appropriately omitted, and theconfigurations different from those in one embodiment will be mainlydescribed.

Modification Example

In the description of one embodiment, an example in which the internalgear 16 has the internal teeth 16 a integrally formed at the innerperipheral portion of the casing 22 has been shown. However, the presentinvention is not limited thereto. The internal gear 16 may be providedwith internally toothed pins made of the same number of metallic pinmembers, instead of the internal teeth 16 a. In this case, the internalgear has an internal gear main body integrated with the casing, and apin member rotatably supported on the internal gear main body. In a casewhere the metallic pin member is used, the casing 22 may be made ofresin such as POM having lower heat resistance than PEEK.

In the description of one embodiment, an example in which two externalgears 14 are provided has been shown. However, the present invention isnot limited thereto. Three or more external gears 14 may be provided.For example, the input shaft may be provided with three eccentricportions 12 a having phases shifted by 120°, and three external gears 14which are oscillated by the three eccentric portions 12 a may beprovided. Further, the number of the external gear 14 may be one.

In the description of one embodiment, an example in which each of thesecond main bearing 26 and the first main bearing 24 has the inner ringhas been shown. However, the present invention is not limited thereto.At least one of the second main bearing 26 and the first main bearing 24may be a bearing having no inner ring.

In the description of one embodiment, an example in which each bearingis a ball bearing having spherical rolling elements has been shown.However, the present invention is not limited thereto. Some or all ofthese bearings may be roller bearings having cylindrical rollingelements.

In the description of one embodiment, an example in which the outputmember is the carrier 18 and the fixed member is the casing 22 has beenshown. However, the present invention is not limited thereto. The fixedmember may be the carrier 18 and the output member may be the casing 22.

In the description of one embodiment, an example in which the firstcarrier 18 and the second carrier 20 are provided has been shown.However, the present invention is not limited thereto. Only the firstcarrier may be provided on one side in the axial direction of theexternal gear.

Each of the modification examples described above exhibits the sameoperation and effect as those of one embodiment.

Any combination of each embodiment and the modification exampledescribed above is also useful as an embodiment of the presentinvention. A new embodiment resulting from the combination also has therespective effects of each embodiment and the modification example whichare combined.

It should be understood that the invention is not limited to theabove-described embodiment, but may be modified into various forms onthe basis of the spirit of the invention. Additionally, themodifications are included in the scope of the invention.

What is claimed is:
 1. An eccentric oscillation type speed reducercomprising: an internal gear; an external gear which meshes with theinternal gear; an eccentric body shaft which oscillates the externalgear; and a carrier disposed at a side portion of the external gear inan axial direction, wherein the carrier includes a first carrier whichis disposed on one side in the axial direction of the external gear, anda second carrier which is disposed on the other side in the axialdirection of the external gear, a driven member is connected to thefirst carrier, the first carrier is made of metal, and the secondcarrier is made of resin.
 2. The eccentric oscillation type speedreducer according to claim 1, further comprising an input shaft bearingwhich is disposed between the first carrier and the eccentric bodyshaft, wherein the input shaft bearing and the eccentric body shaft aremade of metal.
 3. The eccentric oscillation type speed reducer accordingto claim 1, wherein the external gear is made of resin having a higherheat resistance temperature than the second carrier (20).
 4. Theeccentric oscillation type speed reducer according to claim 1, furthercomprising: a carrier pin which connects the first carrier and thesecond carrier; and a spacer which is externally fitted to the carrierpin and is disposed between the first carrier and the second carrier,wherein the carrier pin is made of metal, and the spacer is made ofresin.
 5. The eccentric oscillation type speed reducer according toclaim 1, wherein the first carrier is made of metal having a specificgravity of 5 or less, and the eccentric body shaft is made of iron-basedmetal.
 6. An eccentric oscillation type speed reducer comprising: aninternal gear provided in a casing; an external gear which meshes withthe internal gear; an eccentric body shaft which oscillates the externalgear; and a carrier disposed at a side portion of the external gear inan axial direction, wherein the internal gear comprises: an internalgear main body integrated with the casing, and a pin member which isrotatably supported on the internal gear main body, wherein: theinternal gear main body is made of resin, the casing and the externalgear are made of resin, the carrier is made of metal, and the pin memberis made of metal.